Power supply unit, distributed power supply system and electric vehicle loaded therewith

ABSTRACT

A power supply unit, a distributed power supply system and an electric vehicle loaded therewith, capable of charge/discharge operation are disclosed. A first cell group is connected in parallel to a second cell group in which the electrolytic solution can be electrolyzed or the generated gas can be recombined. A plurality of the parallel circuit pairs are connected in series, and the series circuit is connected with a charger/discharger to constitute the power supply unit. The charger/discharger charges the power supply unit up to a voltage at which the electrolytic solution of the second cell group is electrolyzed or the generated gas is recombined.

BACKGROUND OF THE INVENTION

The present invention relates to a power supply unit comprising amultiplicity of cells such as lithium secondary cells, nickel hydrogencells, lead seal cells, electric double layer capacitors and fuel cellsconnected in series parallel, and a distributed power supply system andan electric vehicle including them.

In the case where a plurality of cells are connected in series, thevariations of capacitance, initial voltage and temperature from one cellto another causes a different voltage for a different cell, therebymaking it difficult for all the series-connected cells to share thevoltage across the circuit uniformly.

Especially in the case where the lithium secondary cells or the electricdouble layer capacitors employing an organic solvent as an electrolyticsolution are connected in series, voltage variations causes anovercharge or an overdischarge, often resulting in a rupture or a fire,or at least an overcharge or an overdischarge, which poses the problemof an extremely shortened service life of the cells.

In order to prevent the overcharge or overdischarge, thecharge/discharge operation may be performed with a pre-set protectivelevel. In charge mode, however, the charge operation stops when thevoltage across a high-voltage cell has reached the protective level. Asa result, the remaining low-voltage cells fail to be fully chargedbefore the end of the charge operation.

In similar fashion, the discharge operation stops at the time point whenthe voltage across a low-voltage cell has reached a protective level. Asa result, the remaining high-voltage cells cannot be fully dischargedbefore the end of the discharge operation.

In the series connection of cells, therefore, the charge/discharge timebecomes shorter than in the case where each cell is charged/dischargedindependently.

In a conventional battery charging apparatus intended to solve thisproblem, the charge current supplied through a bypass is changed by acurrent changing means progressively according as the voltage across thecells being charged approaches a set value thereby to set the cells intoa uniform state. Examples are illustrated in U.S. Pat. No. 5,557,189 anda corresponding Japanese Patent No. JP-A-7-230829. FIG. 12 is a diagramshowing such a battery charging apparatus. In FIG. 12, referencenumerals 1101 a to 1101 c designate cells, numerals 1102 a to 1102 cvoltage detection means, numeral 1103 set voltage application means,numerals 1104 a to 1104 c comparison control means, and numerals 1105 ato 1105 c current changing means. The circuit for the cell 1101 a is soconfigured that the voltage detection means 1102 a, the comparisoncontrol means 1104 a and the current changing means 1105 a are connectedin parallel to each other, and the set voltage application means 1103applies a set voltage indicating the setting of a voltage value of thecell 1101 a.

The present voltage value of the cell 1101 a is detected by the voltagedetection means 1102 a, and compared in the comparison control means1104 a with the set value of the voltage applied by the set voltageapplication means 1103 a. According as the present cell voltageapproaches the set voltage value, the charge current flowing in thecurrent changing means is increased progressively. Specifically, thecharge current to the cell 1101 a is controlled progressively downward.In this way, an overcharge is prevented.

The fact about the cell 1101 a described above equally applies to thecell 1101 b and the cell 1101 c. In other words, the voltage detectionmeans 1102 b, the comparison control means 1104 b and the currentchanging means 1105 b for the cell 1101 b, and the voltage detectionmeans 1102 c, the comparison control means 1104 c and the currentchanging means 1105 c for the cell 1101 c, work exactly the same manneras the corresponding means, respectively, of the cell 1101 a.

Another example of the prior art is disclosed in JP-A-2000-78768. Thisis intended to correct the variations caused at the time of charging thelithium ion secondary cell and to prevent the trouble such as overchargefor an improved service life. Specifically, a negative electrolyticsolution circulation pump and a positive electrolytic solutioncirculation pump are used for correcting the variations of thecharge/discharge operation. Still another example of the prior art isdisclosed in JP-A-2000-511398. This is a system for equalizing the cellsand is a combination of energy storage elements that can be switched.Specifically, the charge is shifted between batteries each including aplurality of cells connected in series. The charge is pulled out of aparticular battery of a higher voltage and transferred to anotherbattery of a lower voltage.

In the conventional battery charging apparatus, a cell voltage at thetime of charging is compared with a set value, and with the approach ofthe cell voltage to the set voltage value, the charge current isprogressively diverted to the current changing means in parallel to thecells thereby to assure uniform conditions of the cells.

According to the prior art, however, the amount of current that can bediverted is greatly limited by the heat generated in the currentchanging means. Thus, the effect of obviating the voltage variationsamong the cells is reduced. The current changing means having a largethermal capacitance through which a large current can flow, on the otherhand, is large in size and the system becomes bulky. Also, an electricalcircuit other than the cells is required and increases the cost. Themethod of circulating the electrolytic solution, on the other hand,requires a pump. Also, a battery equalizer including a switch circuitfor moving the charge by switching and a control circuit for the switchcircuit is required.

SUMMARY OF THE INVENTION

The present invention has been developed in view of the problemsdescribed above, and the object thereof is to provide an inexpensive,compact power supply unit which can correct the voltage variations amongcells connected in series.

According to this invention, there is provided a power supply unitcomprising a first cell group and a second cell group connected inparallel to the first cell group, in which the electrolytic solution ofthe second cell group can be electrolyzed or the generated gas can berecombined. A plurality of the parallel-connected pairs are connected inseries to each other and also to a charger/discharger. Thecharger/discharger is adapted to charge the cells at appropriate timingto a voltage at which the electrolytic solution of the second cells iselectrolyzed or a voltage at which the generated gas is recombined. As aresult, a plurality of parallel-connected pairs including the cells ofthe first cell group and the second cell group are equalized at avoltage at which the electrolytic solution of the cells of the secondcell group is electrolyzed or a voltage at which the generated gas isrecombined.

In the parallel-connected pair of the first cell group and the secondcell group according to the invention, the first cell group and thesecond cell group are connected in parallel through a current limiter.The current limiter limits the current flowing between the first cellgroup and the second cell group, and prevents the overcurrent of thefirst cell group or the second cell group, thereby making it possible toprotect the power supply unit at the time of a fault.

A plurality of series circuits including the parallel-connected pairs ofthe first cell group and the second cell group are connected inparallel. As a result, the capacitance, the output and the service lifeof the power supply unit can be variably increased.

In this invention, the withstanding voltage of the cells of the firstcell group is set to a level higher than the withstanding voltage of thecells of the second cell group. Specifically, the electrolytic solutionof the cells of the second cell group is electrolyzed or the gas isgenerated and recombined within the operating voltage range of the firstcell group. In this way, the cells of the second cell group and thecells of the first cell group are equalized at a voltage at which theelectrolytic solution is electrolyzed or the generated gas isrecombined, as the case may be, in the cells of the second cell group.

According to another aspect of the invention, there is provided a powersupply unit, wherein at least selected one of the first cell group andthe second cell group includes a plurality of cells connected in series.This circuit includes at least an intermediate terminal for eachappropriate number of the series-connected cells, in addition to a mainpositive terminal and a main negative terminal. The first cell group andthe second cell group can be connected in parallel through theintermediate terminal and the main terminals.

According to still another aspect of the invention, there is provided apower supply unit, wherein the first cell group and the second cellgroup share at least one component element. As a result, the number ofparts and the cost are reduced. The component element shared ispreferably the electrolytic solution.

Also, carbon fiber or carbon nanotube is added to the electrodes of atleast selected one of the first cell group and the second cell group.Especially in the batteries with the electrodes thereof extended orcontracted at the time of charge/discharge operation, the resultingstress is relaxed by the carbon fiber or the carbon nanotube, as thecase may be.

According to yet another aspect of the invention, there is provided apower supply unit, wherein the parallel-connected pairs of the firstcell group and the second cell group are connected in parallel to a cellmanagement circuit. As a result, the equalization of the voltage of theparallel-connected pairs can be enhanced and the conditions thereof canbe detected.

According to a further aspect of the invention, there is provided adistributed power supply system in which a cell power supply unitincluding the first cell group and the second cell group is connected inparallel to a second similar power supply unit, the system comprising acharger for performing the charge operation in such a manner that in thecase where the second power supply unit is deficient of power, the firstpower supply unit assists in supplying power, while in the case wherethe second power supply unit generates extra power, the charge operationis continued by a charger, using the extra power, up to a voltage atwhich the electrolytic solution of the cells of the second cell group ofthe first cell power supply unit is electrolyzed or a voltage at whichthe generated gas is recombined.

According a still further aspect of the invention, there is provided anelectric vehicle comprising a motor-generator for driving the vehicleand regenerating power, and a cell power supply unit connected to themotor-generator, wherein the cell power supply unit includes a firstcell group and a second cell group connected in parallel to the firstcell group, the power supply unit further comprising a charger capableof charging the cells of the second cell group up to a voltage where theelectrolytic solution of the cells of the second cell group of the cellpower supply unit is electrolyzed or a voltage at which the generatedgas is recombined.

The invention is applicable to various cells including the lithiumsecondary cells, the nickel-hydrogen cells, the lead seal cells and theelectric double layer capacitors or the fuel cells connected in seriesparallel.

Other objects, features and advantages of the invention will becomeapparent from the following description of the embodiments of theinvention taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing a first embodiment of the invention.

FIGS. 2A and 2B are diagrams for explaining the basic operation of theinvention.

FIG. 3 is a diagram showing a second embodiment of the invention.

FIG. 4 is a diagram showing a third embodiment of the invention.

FIG. 5 is a diagram showing a fourth embodiment of the invention.

FIGS. 6A and 6B are diagrams showing a fifth embodiment of theinvention.

FIG. 7 is a diagram showing a sixth embodiment of the invention.

FIG. 8 is a diagram showing a seventh embodiment of the invention.

FIG. 9 is a diagram showing an eighth embodiment of the invention.

FIG. 10 is a diagram showing a power system combined with a solar powerconversion apparatus using a power supply unit embodying the invention.

FIG. 11 is a diagram showing an example of an electric vehicle using apower supply unit embodying the invention.

FIG. 12 is a diagram showing a conventional battery charging apparatus.

DESCRIPTION OF THE INVENTION

Embodiments of the invention will be explained below in detail withreference to the accompanying drawings. FIG. 1 is a diagram showing anembodiment of the invention. In FIG. 1, reference numeral 101 designatesfirst cell group (101 a to 101 n), numeral 102 a second cell group (102a to 102 n), numeral 103 a charger/discharger, and numeral 104 a powersupply/load. One first cell 101 (101 a) and two second cells 102 (102 a,102 b) are connected in parallel, and a plurality of the parallelcircuits are connected in series. The series-connected cell groups areconnected to the charger/discharger 103 and constitute a power supplyunit. This power supply unit is connected to the power supply/load 104.

In FIG. 1, the first parallel circuit including the first cell 101 a andthe second cells 102 a, 102 b and the second parallel circuit connectedin series to the first parallel circuit and including the first cell 101b and the second cells 102 c, 102 d, i.e. the two series-connectedstages, indicated by solid lines, constitute a minimum unit circuit ofthe invention. This configuration can assure a charge balance betweenthe first cells 101 a, 101 b. Further, the number of the stages of theseries-connection is increased to 3, 4 and so on for practicalapplications. The first cell group 101 includes lithium secondary cellsor electrical double layer capacitors, while the second cell group 102includes lead cells, nickel hydrogen cells, nickel cadmium cells andfuel cells capable of electrolyzing the electrolytic solution,generating and recombining the gas and refilling the electrolyticsolution.

The charger/discharger 103 can be configured of a bidirectional DC/DCconverter or a unidirectional charge DC/DC converter paired with adischarge DC/DC converter. This charger/discharger 103 controls thevoltage and the current as suitable for the cells and the powersupply/load 104. The power supply/load 104 is a commercial power supply,a generator or an ordinary electrical equipment. The charger/discharger103 appropriately charges the second cells 102 up to a voltage at whichthe electrolytic solution is electrolyzed or at which the generated gasis recombined. As described above, the first cell group 101 and thesecond cell group 102 are connected in parallel, and these parallelcircuits are connected in series to each other at least in two stages.Thus, the voltages of the first cells 101 in the configuration indicatedby solid lines in FIG. 1 can be equalized by the voltage at which theelectrolytic solution of the second cells is electrolyzed or at whichthe generated gas is recombined.

Now, the operation of equalizing the voltages of the first cells by thevoltage at which the electrolytic solution of the second cells iselectrolyzed or at which the generated gas is recombined, will beexplained with reference to the equivalent circuit shown in FIG. 2A. InFIG. 2A, (a) represents a basic configuration of the first cell group101 and the second cell group 102, i.e. the portion defined by the solidlines in FIG. 1, while (b) represents an equivalent circuit forexplaining the operation. Numerals 10 a to 10 d designate elementshaving the zener diode characteristics, for example. Numerals 16 a to 16d designate comparators, and characters Va to Vd zener voltages. In thecase where the second cells come to assume a predetermined voltage byovercharge, i.e. the zener voltages Va to Vd are reached in theequivalent circuit, the comparators 16 a to 16 d turn off, closeswitches 12 a to 12 d and connect resistors 14 a to 14 d. The firstcells 101 and the second cells 102 are equalized, or especially, thevoltages of the first cells are equalized. The resistors 14 a to 14 dhave the same resistance value. The second cells perform the operationsimilar to the equivalent circuit described above, and therefore thefirst cells 101 (101 a, 101 b) can be equalized.

In this way, the first cells 101 are combined with the second cells 102,i.e. high-output cells are combined with large-capacitance cells torealize a power supply unit apparently having a high output and a largecapacitance. For example, the lithium secondary cell having a highoutput is used for the first cells 101, and the lead seal cell having alarge capacitance is used for the second cells 102. In this case, twolead seal cells (102 a, 102 b) in series and one lithium secondary cell(101 a) are connected in parallel to each other. This parallel circuitis further connected in series with another parallel circuit of the twolead seal cells (102 c, 102 d) and the one lithium secondary cell (101b).

By doing so, the voltage (overcharge voltage) of the lead seal cell atwhich the electrolytic solution is electrolyzed or at which thegenerated gas is recombined is about 2.1 V, or about 4.2 V for two suchparallel circuits connected in series. On the other hand, the upperlimit (withstanding voltage) of the operating voltage range of thelithium secondary cell is about 4.3 V. Therefore, the lead seal cellsand the lithium secondary cells are equalized at 2.1 V x 2 and 4.2 V,respectively, by the overcharged state of the lead seal cells. In otherwords, the terminal voltage of the series-connected lead seal cells isequalized at 4.2 V, and the terminal voltage of the lithium secondarycells at 4.2 V.

The lead seal cell, though inexpensive and large in capacitance, cannotbe charged with large current, and if charged with an unreasonably largecurrent, the service life thereof would be extremely shortened. Thelithium secondary cell, on the other hand, can be charged with largecurrent, but the cost thereof increases comparatively if increased incapacitance. By combining these two types of cells, both a high outputand a large capacitance can be realized with a longer service life and alower cost. This is schematically shown in FIG. 2B. The ordinaterepresents the output, which corresponds to the charge current. In otherwords, the first cells can be used for large-output applications, andthe second cells for large-capacitance applications.

The graph of FIG. 2B also indicates that the ordinate representing thecharge current, the first cells can be charged with large current for ashort time, while the second cells are required to be charged with acomparatively small current for long hours. Specifically, the parallelconnection of the first cell group and the second cell group makespossible cells having the dual characteristics of large output and largecapacitance. These cells can be charged with a large current, andtherefore, for applications to an electric vehicle described later, thecharge operation can be performed by effectively utilizing the powerregenerated in power regeneration mode.

FIG. 3 is a diagram showing a second embodiment of the invention. InFIG. 3, numeral 201 designates a current limiter. The first cells 101and the second cells 102 are connected in parallel to each other throughthe current limiters 201. FIG. 3 represents a case in which electricaldouble layer capacitors 101 cpa to 101 cpn are used as the first cells101.

The current limiters 201 are each a PTC (positive thermal conductor)having such a characteristic as to increase the resistance with a largecurrent, a resistor or a fuse. The current limiters 201 limit thecurrent flowing between the first cells 101 and the second cells 102(the current flowing from the first cells to the second cells, and thecurrent flowing in the reverse direction) and thereby prevent anovercurrent from flowing in the cells. Also, the parallel-connectedcells are prevented from being shorted in chain in the case where thefirst cells 101 or the second cells 102 are shorted.

FIG. 4 is a diagram showing a third embodiment of the invention. In FIG.4, the parallel circuit of the first cells 101 and the second cells 102shown in FIG. 1 and (a) in FIG. 2 is connected in parallel to anothersimilar parallel circuit. The charger/discharger 103 and the powersupply/load 104 are also connected. A plurality of series-connectedcircuits are connected in parallel in this way, so that the capacitance,the output and the service life of the power supply unit can be variablyincreased.

Also, as in the first embodiment, the charger/discharger 103 performsthe charge operation, at an appropriate timing, up to a voltage at whichthe electrolytic solution of the second cells 102 is electrolyzed or atwhich the generated gas is recombined.

As a result, in a plurality of the parallel circuits of the first cells101 and the second cells 102 in series, the second cells 102 areequalized at a voltage at which the electrolytic solution of the secondcells 102 is electrolyzed or at which the generated gas is recombined.In FIG. 4, the portion (a) corresponds to FIG. 1 or the portion (a) inFIG. 2A, while the portion (b) corresponds to the configuration of FIG.3. These portions are connected in parallel to configure the circuit ofFIG. 4.

FIG. 5 is a diagram showing a fourth embodiment of the invention. InFIG. 5, the electrical double layer capacitors 101 cpa to 101 cpn andthe lithium secondary cells 101La to 101Ln constituting the first cells101, are connected in parallel to each other. Assuming that the lithiumsecondary cell is a third cell, this represents a case in which thelithium secondary cells constituting the first cells are used as thethird cells. The first cell 101 and the second cell 102 are connected inparallel to each other through the corresponding current limiter 201.The series circuit including these parallel circuits is connected to thecorresponding charger/discharger 103, thereby constituting a powersupply unit.

The withstanding voltage of the first cells 101 (101 cpa to 101 cpn) andthe third cells is set to a value higher than the withstanding voltageof the second cells 102. Specifically, the voltage can be equalizedwithin the range of the operating voltage of the first cells 101 (101cpa to 101 cpn) and the third cells (101La to 101Ln). More specifically,the second cells 102 are charged up to a voltage at which theelectrolytic solution is electrolyzed or the generated gas isrecombined, while the second cells 102 and those first cells 101 whichconstitute the third cells (101La to 101Ln) are charged for equalizationup to a voltage at which the electrolytic solution is electrolyzed orthe generated gas is recombined.

Assume that the first cells 101 (101 cpa to 101 cpn) are the electricaldouble layer capacitors having a withstanding voltage of 3.5 V, and thesecond cells 102 are the nickel hydrogen cells in which the electrolyticsolution is electrolyzed or the gas is generated at a voltage of 1.6 V,and the third cells are the lithium secondary cells having awithstanding voltage of 4.3 V. The electrical double layer capacitorsand the lithium secondary cells are equalized at 3.6 V by the overchargeof the nickel hydrogen cells.

FIGS. 6A and 6B are diagrams showing a fifth embodiment of theinvention. In FIG. 6A, numeral 501 designates a positive terminal,numeral 502 a negative terminal, numeral 503 a case and numeral 504intermediate terminals. A plurality of the first cells 101 or the secondcells 102 are connected in series and accommodated in the case 503. Theends of the series circuit are provided with the positive terminal 501and the negative terminal 502 for transmitting and receiving power.Further, the intermediate terminal 504 is arranged for eachseries-connected two cells.

Additional first cells 101 or second cells 102 can be connected inparallel to this circuit through the intermediate terminals 504, thepositive terminal 501 and the negative terminal 502. FIG. 6B is themanner in which the cells accommodated in the cases 503 a, 503 b areconnected in parallel. Numerals 504 a 1, 504 a 2 designate theintermediate terminals of the cells accommodated in the case 503 a.Numerals 504 b 1 and 504 b 2 designate the intermediate terminals of thecells accommodated in the case 503 b. By interconnecting theseterminals, the series circuits shown in FIG. 6A can be connected inparallel to each other.

FIG. 7 is a diagram showing a sixth embodiment of the invention. In FIG.7, numeral 601 designates a positive electrode a, numeral 602 aseparator a, numeral 603 a negative electrode a, and numeral 604 apartitioning wall, the components making up the first cell 101. Also,numeral 605 designates a positive electrode b, numeral 606 a separatorb, and numeral 607 a negative electrode b, all the component partsmaking up the second cell 102. Numeral 608 designates a positive leadwire, and numeral 609 a negative lead wire.

The positive electrode a 601, the separator a 602 and the negativeelectrode a 603 are arranged in that order and immersed in theelectrolytic solution (not shown), thereby making up a part of thecomponent elements of the first cell 101. Also, the positive electrode b605, the separator b 606 and the negative electrode b 607 are arrangedin that order, and immersed in the electrolytic solution (not shown),thereby constituting a part of the component elements of the second cell102.

These component elements are separated from each other spatially by thepartitioning wall 604 and accommodated in a common case 503. Also, thepositive electrode a 601, the positive electrode b 605 and the positiveterminal 501 are connected by the positive lead wire 608. In similarfashion, the negative electrode b 603, the negative electrode b 607 andthe negative terminal 502 are connected by the negative lead wire 609.

In this case, as compared with the configuration in which the first cell101 and the second cell 102 are configured independently of each other,each of the component elements such as the positive terminal 501, thenegative terminal 502, the positive lead wire 608, the negative leadwire 609 and the case 503 is shared, which make up a parallel circuitpair. Further, though not shown, a protective mechanism and protectivedevices including an explosion-proof valve and a pressure switch canalso be shared. As a result, the number of parts and the power cost canbe reduced.

FIG. 8 is a diagram showing a seventh embodiment of the invention. InFIG. 8, the partitioning wall 604 of FIG. 6 is not included, and thecomponent elements of the first cell 101 and the second cell 102 areaccommodated in the same space. As a result, the electrolytic solutionis also shared. This configuration can be realized by employing theaqueous solution of sulfuric acid as the electrolytic solution, theelectrical double layer capacitor as the first cell 101, and the leadseal cell as the second cell 102. A similar configuration can be alsorealized by employing the aqueous solution of potassium hydroxide as theelectrolytic solution, the electrical double layer capacitor as thefirst cell 101 and the nickel hydrogen cell as the second cell 102.

In the case under consideration, the electrodes of the first cell 101and the second cell 102 and the separators 602, 606 are shown inlaminate. Nevertheless, they can be implemented with otherconfigurations such as in winding.

As an eighth embodiment of the invention, carbon fiber or carbonnanotube is desirably added to at least one of the electrodes(generally, a negative electrode) of the first cell 101 and the secondcell 102 shown in FIG. 7 or 8. The use of the lithium secondary cell orthe lead cell is accompanied by the expansion/contraction of theelectrodes at the time of charge or discharge. The electrical doublelayer capacitor and the nickel hydrogen cell, on the other hand, are notaccompanied by the expansion/contraction of the electrodes at the timeof charge or discharge. In the case where these cells are accommodatedin a common space, stress is exerted also on the electrical double layercapacitor and the nickel hydrogen cell for a considerably deterioratedperformance. In view of this, carbon fiber or carbon nanotube is addedto an electrode (generally, a negative electrode) thereby to relax thestress and prevent the performance deterioration.

FIG. 9 is a diagram showing a ninth embodiment of the invention. In FIG.9, a cell controller 807 is configured of cell management circuits 801 ato 801 c, voltage detection circuits 802 a to 802 c, potentialconversion circuits 803 a to 803 c, a processing circuit 804, aninsulating circuit 805 and a communication circuit 806. The first cells101 cpa to 101 cpc are connected in parallel to the second cells 102 a,102 b; 102 c, 102 d; 102 e, 102 f, respectively. A plurality of theseparallel circuits (three stages in the case of FIG. 9) are furtherconnected in series. Also, the cell management circuit 801 is connectedin parallel to each of the parallel circuit pair (the second cells 102a, 102 b with the first cell 101 cpa, for example) including the firstcells 101 and the second cells 102.

The cell management circuit 801 (801 a to 801 c) is connected to theprocessing circuit 804 through the potential conversion circuit 803 (803a to 803 c). The processing circuit 804 is connected also to thecommunication circuit 806 through the insulating circuit 805. Thesecomponent parts make up the cell controller 807.

The potential conversion circuit 803 (803 a to 803 c) converts thepotential level of each parallel circuit detected by the cell managementcircuit 801 (801 a to 801 c) and transmits an electrical signal. Basedon the terminal voltage of each parallel circuit pair, the processingcircuit 804 determines the charged condition and the voltage balance ofeach parallel circuit pair, detects the residual discharge amount andthe allowable input/output, and drives a bypass circuit. Also, theinformation signals including the allowable residual discharge value andthe allowable input/output, after being insulated electrically in theinsulating circuit 805, are transmitted through the communicationcircuit 806 to the power supply/load 104 or the charger/discharger 103.Character TX of the communication circuit designates transmission means,and RX receiving means.

The cell management circuit 801 (801 a to 801 c) has a voltage detectioncircuit 802 (802 a to 802 c) and a bypass circuit (not shown) fordetecting the terminal voltage of each parallel circuit pair. Also,though not shown, the bypass circuit can be controlled to obviate thevoltage imbalance of each parallel circuit pair.

The voltage imbalance is obviated, through the charger/discharge 103described above, by equalization using a voltage at which theelectrolytic solution of the second cells 102 of the second cells 102 iselectrolyzed or a voltage at which the generated gas is recombined. Inthis way, by use of a bypass circuit, the size can be reduced and theeffect of equalization is enhanced.

FIG. 10 shows a power supply system according to an embodiment of theinvention, and is a diagram showing a distributed power supply systemcombined with the apparatus for converting the solar light into electricpower according to an embodiment. In FIG. 10, numeral 901 designates acommercial power supply, numeral 902 a solar power generating apparatus,numerals 903 a, 90 b load units, numeral 904 a control converter, andnumerals 905 a, 905 b, 905 c switches. In FIG. 10, the first cells 101 ato 101 d are connected in parallel to the second cells 102 a, 102 b to102 g, 102 h. A plurality of (four, in this embodiment) these parallelcircuit pairs are further connected in series, and the series circuit isconnected to the cell controller 807.

Also, the positive terminal 501 and the negative terminal 502 of theseries circuit are connected to the control converter 904 correspondingto the charger/discharger 103 on the one hand, and the communicationcircuit 806 in the cell controller 807 is connected to the MCU in thecontrol converter 904 at the same time.

Further, the commercial power supply 901, the solar power generatingapparatus 902 and the load unit 903 corresponding to the powersupply/load 104 are connected through the switches 905 a to 905 d to thecontrol converter 904. Also, the solar power generating apparatus 902,the load unit 903, the control converter 904, the switches 905 a to 905d and the cell controller 807 are connected to each other throughbidirectional communication. The solar power generating apparatus 902converts the solar light into DC power by a solar battery and outputs ACpower through an inverter unit (INV).

The load unit 903 a is a home electric appliance such as anair-conditioner, a refrigerator, an microwave oven or lightingequipment, or an electrical equipment such as a motor, an elevator, acomputer or a medical equipment. The load unit 903 b may be a secondpower supply unit. The control converter 904 is a charger/discharger forconverting AC power to DC power or the other way around. A controllerMCU controls the charge/discharge operation, the solar power generatingapparatus 902 and the load unit 903. The MCU outputs a control signal tothe switches 905 a to 905 d.

These devices may have a switch 905 within it. Also, the power supplyunit according to the invention may be connected with the controlconverter 904 and other devices of other than the device configurationshown. According to this embodiment, the power required of the load unit903, if it cannot be afforded by the commercial power supply 901 or thesolar power generating apparatus 902, can be supplied from the cellsthrough the control converter 904. As long as the power from thecommercial power supply 901 or the solar power generating apparatus 904is in oversupply, the power is stored in the cells through the controlconverter 904.

In the case where the terminal voltage of the cells reaches a dischargestop level or a charge stop level during the aforementioned operation,the cell controller 807 transmits the particular signal to the controlconverter 904, which controls the charge/discharge operation. Also, upondetection of a voltage imbalance of the cells, a bypass circuit, if any,is controlled to obviate the voltage imbalance.

Upon detection that the voltage imbalance is of such a level that cannotbe obviated by the bypass circuit, the commercial power supply 901, thesolar power generating apparatus 902, the load unit 903, the controlconverter 904 and the switch 905 are controlled to equalize at a voltageat which the electrolytic solution of the second cells 102 iselectrolyzed or at which the generated gas is recombined. According tothese embodiments, the contract power demand or the power consumption ofthe commercial power supply 901 or the power generation rating of thesolar power generating apparatus 902 can be reduced, thereby saving theequipment expenditure and the running cost.

Also, during a certain time zone when the power consumption isconcentrated, power is supplied from the power supply unit to thecommercial power supply 901, while when the power consumption is small,the power is accumulated in the power supply unit. In this way, theconcentration of the power consumption can be relaxed and the powerconsumption can be averaged out. Further, the MCU of the controlconverter 904 controls the load unit 903 by monitoring the powerconsumption of the load unit 903, and therefore the power is saved andthe effective power utilization are achieved.

FIG. 11 shows an example of an electric vehicle using a power supplyunit according to the invention. In FIG. 11, numeral 1001 designates amotor-generator for driving the vehicle, and numeral 1002 a DC loadunit. The motor-generator 1001 is connected through the controlconverter 904 to the series circuit of a plurality of the cells. Themotor-generator 1001 starts the engine, assists in supplying the driveforce (powering) and generates power (regeneration). In powering mode,power is supplied from the power supply unit to the motor-generator1001. In regeneration mode, on the other hand, power is supplied fromthe motor-generator 1001 to the power supply unit.

Also, the DC load unit 1002 is an electric load such as a solenoid valveor an audio equipment or a second power supply unit. The DC load unit1002 is connected in series to the cells through the switch 905.

As a result, a vehicle can be realized in which the engine can beassisted in torque at the time of starting, and generative energy isconverted to electric power and stored when braking the vehicle.Especially, this power supply unit uses the first cells, and thereforecan be charged with large current. Thus, at the time of regeneration,the regenerative energy can be effectively utilized as charge power.This compares with the prior art, in which what is called the quickcharge has been impossible, and therefore the corresponding portion hasconstituted thermal loss.

With the power supply unit according to the invention, the voltages ofthe cells connected in series parallel can be equalized on the one hand,and the power supply unit can be used as a distributed power supplysystem. Also, the application of the invention to an electric vehiclemakes it possible to effectively utilize the regenerative power ascharge power for the power supply unit.

It should be further understood by those skilled in the art that theforegoing description has been made on embodiments of the invention andthat various changes and modifications may be made in the inventionwithout departing from the spirit of the invention and scope of theappended claims.

1-10. (canceled)
 11. A motor vehicle comprising: a storage batterycomprising a plurality of circuits connected in series, each of theplurality of circuits including a first cell group and a second cellgroup connected in parallel; wherein said second cell group utilizes anelectrolyzable electrolytic solution or generates recombinable gas; apower supply unit including a charger/discharger for controllingcharge/discharge of said storage battery, and adapted to charge saidstorage battery up to a voltage at which the electrolytic solution ofsaid second cell group is electrolyzed or a voltage at which thegenerated gas is recombined; and a motor-generator for driving a motorby electric power supplied by said power supply unit when said motorvehicle is in a powering mode, and for generating electric power whensaid motor vehicle is in a regeneration mode; wherein when said motorvehicle generates electric power, said storage battery is charged by theelectric power of said motor-generator up to a voltage at which theelectrolytic solution of said second cell group is electrolyzed or avoltage at which the generated gas is recombined; and wherein the firstcell group includes lithium secondary cells or electrical double layercapacitors, and the second cell group includes lead cells, nickelhydrogen cells, nickel cadmium cells or fuel cells.
 12. A motor vehicleaccording to claim 11, wherein said first cell group and second cellgroup are connected in parallel through a current limiter.
 13. A motorvehicle according to claim 11, further comprising a plurality of saidstorage batteries connected in parallel.